The Enhanced Durability of AgCu Nanoparticle Coatings for Antibacterial Nonwoven Air Conditioner Filters.

Antibacterial nonwoven fabrics, incorporated with Ag, have been applied as masks and air conditioner filters to prevent the spread of disease from airborne respiratory pathogens. In this work, we present a comparison study of Ag ions: Ag and AgCu nanoparticles (NPs) coated onto nonwoven fabrics intended for use as air conditioner antibacterial filters. We illustrate their color changes and durability running in air conditioners using antibacterial activity testing and X-ray Photoelectron Spectroscopic (XPS) analysis. We found that AgCu NPs showed the best antibacterial efficacy and durability. XPS analysis indicated that the Ag concentration, on both the AgCu and Ag- NP-coated fibers, changed little. On the contrary, the Ag concentration on Ag ion-coated fibers decreased by ~30%, and the coated NPs aggregated over time. The color change in AgCu NP-coated fabric, from yellow to white, is caused by oxide shell formation over the NPs, with nearly 46% oxidized silver. Our results, both from antibacterial evaluation and wind blowing tests, indicate that AgCu NP-coated fibers have higher durability, while Ag ion-coated fibers have little durability in such applications. The enhanced durability of the AgCu NP-coated antibacterial fabrics can be attributed to stronger NP-fiber interactions and greater ion release.

AgCu NP Formation by the Ag NP Catalysis of Cu Ions at Room Temperature and Their Antibacterial Efficacy: A Kinetic Study.

Although a facile route to prepare AgCu nanoalloys (NAs) with enhanced antibacterial efficacy using Ag NP catalysis of Cu ions at elevated temperatures was previously developed, its detailed reaction process is still unclear due to the fast reaction process at higher temperatures. This work found that AgCu NAs can also be synthesized by the same process but at room temperature. AgCu NAs formation kinetics have been studied using UV-Visible spectra and Transmission Electron Microscopy (TEM), where formation includes Cu2+ deposition onto the Ag NP surface and Ag+ release, reduction, and agglomeration to form new Ag NPs; this is followed by a redistribution of the NA components and coalescence to form larger AgCu NPs. It is found that SPR absorption is linear with time early in the reaction, as expected for both pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetics; neither model is followed subsequently due to contributions from newly formed Ag NPs and AgCu NAs. The antibacterial efficacy of the AgCu NAs thus formed was estimated, with a continuous increase over the whole alloying process, demonstrating the correlation of antibacterial efficacy with the extent of AgCu NA formation and Ag+ release.

Human alveolar epithelial cell responses to core-shell superparamagnetic iron oxide nanoparticles (SPIONs).

Superparamagnetic iron oxide nanoparticles (SPIONs) have been prepared and coated with positively (-NH3(+)) and negatively (-COO(-)) charged shells. These NPs, as well as their "bare" precursor, which actually contain surface hydroxyl groups, have been characterized in vitro, and their influence on a human epithelial cell line has been assessed in terms of cell metabolic activity, cellular membrane lysis, mitochondrial activity, and reactive oxygen species production. Their physicochemical characterizations and protein-nanoparticle interactions have been determined using dynamic light scattering, high-resolution transmission electron microscopy, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) spectrometry, and Coomassie Blue fast staining. Cell-SPION interactions have been determined by PrestoBlue resazurin-based, Trypan Blue dye exclusion-based, and MTS cell proliferation assays as well as by reactive oxygen species determination. The results show that different surface characteristics cause different protein corona and cell responses. Some proteins (e.g., albumin) are adsorbed only on positively charged coatings and others (e.g., fibrinogen) only on negatively charged coating. No cell deaths occur, but cell proliferation is influenced by surface chemistry. Proliferation reduction is dose dependent and highest for bare SPIONs. Negatively charged SPIONs were the most biocompatible.

Comment on "High-Resolution Microscopical Studies of Contact Killing Mechanisms on Copper-Based Surfaces".

In the original paper, Chang and co-workers describe the contact killing of Bacillus subtilis, a Gram-positive bacterium, on copper-containing substrates and offer a mechanism for its accomplishment. The present Comment offers support for that mechanism and adds a necessary initial step, the degradation of the overlying peptidoglycan lattice. Degradation is necessary because the lattice is too thick, and its pores too small, for substrate-membrane contact without it. A suggestion is offered as to how degradation is accomplished.

Cytotoxicity and Antibacterial Efficacy of AgCu and AgFe NanoAlloys: A Comparative Study.

Although Ag nanoparticles (NPs) have been widely applied in daily life and in biomedical and industrial fields, there is a demand for Ag-based bimetallic nanoalloys (NAs), such as AgCu and AgFe, due to their enhanced antibacterial efficacy and reduced Ag consumption. In this work, we present a comparison study on the antibacterial efficacy and cytotoxicity rates of Ag NPs and AgCu and AgFe NAs to L929 mouse fibroblast cells using the CCK-8 technique based on the relative cell viability. The concept of the minimum death concentration (MDC) is introduced to estimate the cytotoxicity to the cells. It is found that the minimum inhibitory concentrations (MICs) of the NPs against E. coli and S. aureus decrease with the addition of both Cu and Fe. There is a strong correlation between the MDC and MIC, implying that the mechanisms of both antibacterial efficacy and cytotoxicity are similar. The enhanced antibacterial efficacy to bacteria and cytotoxicity toward the cell are attributed to Ag+ release. The following order is found for both the MIC and MDC: AgFe < AgCu < Ag NPs. However, there is no cytotoxicity to the L929 cells for AgFe and AgCu NAs at their MIC Ag concentrations against S. aureus.

A Pragmatic Perspective of the Antibacterial Properties of Metal-Based Nanoparticles.

A consideration of the antibacterial efficacy of metal-based nanoparticles, from the point of view of their physicochemical properties, suggests that such efficacy arises from the protein coronas that form around them, and that the contents of the coronas depend on the chemical groups found on the nanoparticle surfaces. We offer a new perspective and new insights, making use of our earlier observations of the physicochemical properties of nanoparticle surfaces, to propose that the nanoparticle serves as a mediator for the formation and activation of the protein corona, which attacks the bacterium. That is, the nanoparticle enhances the body's natural defenses, using proteins present in body fluids.

Antimicrobial Properties of the Ag, Cu Nanoparticle System.

Microbes, including bacteria and fungi, easily form stable biofilms on many surfaces. Such biofilms have high resistance to antibiotics, and cause nosocomial and postoperative infections. The antimicrobial and antiviral behaviors of Ag and Cu nanoparticles (NPs) are well known, and possible mechanisms for their actions, such as released ions, reactive oxygen species (ROS), contact killing, the immunostimulatory effect, and others have been proposed. Ag and Cu NPs, and their derivative NPs, have different antimicrobial capacities and cytotoxicities. Factors, such as size, shape and surface treatment, influence their antimicrobial activities. The biomedical application of antimicrobial Ag and Cu NPs involves coating onto substrates, including textiles, polymers, ceramics, and metals. Because Ag and Cu are immiscible, synthetic AgCu nanoalloys have different microstructures, which impact their antimicrobial effects. When mixed, the combination of Ag and Cu NPs act synergistically, offering substantially enhanced antimicrobial behavior. However, when alloyed in Ag-Cu NPs, the antimicrobial behavior is even more enhanced. The reason for this enhancement is unclear. Here, we discuss these results and the possible behavior mechanisms that underlie them.

Physicochemical Characterization of Polyvinyl Pyrrolidone: A Tale of Two Polyvinyl Pyrrolidones.

Of several samples of polyvinyl pyrrolidone (PVP) used to coat and stabilize freshly manufactured aqueous dispersions of silver nanoparticles, one batch gave anomalous results: the dispersion maintained continued stability, even on extensive dilution. Our efforts to understand this desirable feature concluded that the generally used spectral method of PVP purity verification, Fourier transform infrared (FTIR) spectroscopy, was incapable of answering our inquiry. This led to the employment of several other methods, including X-ray photoelectron and nuclear magnetic resonance spectroscopies, which ultimately revealed several possible reasons for the dilution stability, including incomplete PVP hydrolysis during manufacture and the presence of hydroperoxide contaminants. It led, as well, to explanations for the shortcomings of FTIR spectroscopy as a verification method for PVP purity.

Adhesion to tooth structure mediated by contemporary bonding systems.

Given the enormity of the field of adhesion and the number of commercial products available, the discipline of modern adhesive dentistry can be daunting with respect to materials and techniques. This article organizes contemporary bonding practice and materials around an understanding of the fundamentals of adhesion to tooth structure. In providing this context, adhesive development, bonding systems, and their appropriate use are better understood. The end result is the better practice of adhesive dentistry.

Characterization of endotoxins on orthopaedic fixation screws, using physicochemical surface analyses.

The objective of this study was to determine if surface analysis techniques could be used to detect endotoxin on stainless steel malleolus screws. New malleolus screws were compared to ones that had been coated in purified lipopolysaccharide (LPS) or Artificial Test Soil (ATS) containing lipopolysaccharide. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and time-of flight secondary ion mass spectrometry (TOF-SIMS) were used to assess the fixation screws surface. Organic material was visualized on the LPS and ATS-LPS inoculated screws but not on the new unsoiled screws. This was further supported by the peaks observed at masses between 40 and 100 D in TOF-SIMS spectra of the LPS and ATS-LPS inoculated screws. After deconvolution of N1s high resolution XPS spectra, the LPS inoculated screws showed amide groups whereas the ATS-LPS inoculated screws showed predominantly nitroso groups (C-NO). Our data demonstrate that surface analysis can be used to detect organic residuals present on fixation screws. The XPS data confirmed that LPS reacted predominantly with positively charged surface metallic ions (Fe and Cr), whereas proteins reacted with the surface oxide layer of fixation screws, forming C-NO groups. The application of these surface analysis techniques will be helpful in determining if the reprocessing of such items results in an accumulation of organic material that might lead to aseptic loosening, when implanted. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:240-247, 2017.

A comparative physicochemical, morphological and magnetic study of silane-functionalized superparamagnetic iron oxide nanoparticles prepared by alkaline coprecipitation.

The characterization of synthetic superparamagnetic iron oxide nanoparticle (SPION) surfaces prior to functionalization is an essential step in the prediction of their successful functionalization, and in uncovering issues that may influence their selection as magnetically targeted drug delivery vehicles (prodrugs). Here, three differently functionalized magnetite (Fe3O4) SPIONs are considered. All were identically prepared by the alkaline coprecipitation of Fe(2+) and Fe(3+) salts. We use X-ray photoelectron spectroscopy, electron microscopy, time-of-flight SIMS, FTIR spectroscopy and magnetic measurements to characterize their chemical, morphological and magnetic properties, in order to aid in determining how their surfaces differ from those prepared by Fe(CO)5 decomposition, which we have already studied, and in assessing their potential use as drug delivery carriers.

Washing effect on superparamagnetic iron oxide nanoparticles.

Much recent research on nanoparticles has occurred in the biomedical area, particularly in the area of superparamagnetic iron oxide nanoparticles (SPIONs); one such area of research is in their use as magnetically directed prodrugs. It has been reported that nanoscale materials exhibit properties different from those of materials in bulk or on a macro scale [1]. Further, an understanding of the batch-to-batch reproducibility and uniformity of the SPION surface is essential to ensure safe biological applications, as noted in the accompanying article [2], because the surface is the first layer that affects the biological response of the human body. Here, we consider a comparison of the surface chemistries of a batch of SPIONs, before and after the supposedly gentle process of dialysis in water.

Spectroscopic evidence for pi-pi interaction between poly(diallyl dimethylammonium) chloride and multiwalled carbon nanotubes.

The interaction between multiwalled carbon nanotubes (MWCNTs) and aqueous poly(diallyl dimethylammonium) chloride (PDDA) was studied by X-ray photoelectron (XPS) and photoacoustic Fourier transform infrared (PA-FTIR) spectroscopies. We have found that the mild sonication of MWCNTs in aqueous PDDA results in a significant improvement of CNT dispersibility and greatly enhances their adhesion to Au and Si substrates. The MWCNT-PDDA interaction is due to the presence of an unsaturated contaminant in the PDDA chain, as confirmed by both XPS and PA-FTIR, which enters into a pi-pi interaction with the CNTs. Electrostatic group repulsions of the coated CNTs then provide the dispersibility and adhesion.

Functionalization of multiwalled carbon nanotubes by mild aqueous sonication.

Sonication has been widely used in the dispersal of carbon nanotubes (CNTs) in various liquids as well as in their functionalization in aqueous acids. Here, for the first time, we study the sonication of multiwalled CNTs (MWCNTs) in deionized water. Our results indicate an improvement in the aqueous dispersal of MWCNTs as well as an increase in their adhesive interaction with Au substrates. Field emission scanning electron and high-resolution transmission electron microscopies as well as X-ray photoelectron, photoacoustic Fourier transform IR, and Raman spectroscopies have shown this to be due to the production of low concentrations of O-containing functionalizations (alcohol, carbonyl, acid, with the total O concentration being approximately 2%), without damaging the basic CNT structure; this production of functional groups is mirrored by the disappearance of -CH(n) groups existing on the pristine CNTs. These new functional groups are capable of hydrogen bonding, which plays an important role in their aqueous dispersal and enhanced substrate interactions.

Oxidation, deformation, and destruction of carbon nanotubes in aqueous ceric sulfate.

A simple wet chemical method involving only ultrasonic processing in dilute ceric sulfate (CS) was used to functionalize carbon nanotubes (CNTs). Unexpectedly, single-walled and multiwalled carbon nanotubes (SWCNTs and MWCNTs) were cut, oxidized, and disintegrated by sonication in 0.1 N CS for 2-5 h. Transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction spectroscopy (XRD), Raman scattering, and photoacoustic Fourier transform infrared spectroscopy (FTIR) were used to probe wall damage during the chemical processing. Cyclic voltammetry and impedance spectroscopy were used to evaluate the conductivity of the CS-treated CNTs. This one-step process resulted in the destruction of SWCNTs to produce nonconducting amorphous carbon. MWCNTs were oxidized and converted to graphitic materials and amorphous carbon with retained conductivity.

Electrophoretic separation of aniline derivatives using fused silica capillaries coated with acid treated single-walled carbon nanotubes.

This paper reports on a new strategy for coating fused silica capillaries based on the ionic adsorption of acid treated single-walled carbon nanotubes (SWCNTs) on a poly(diallydimethylammonium chloride)-modified fused silica surface. The coated capillaries were used to demonstrate their performance for baseline separation of a mixture of seven nitrogen-containing aromatic compounds compared to capillary zone electrophoresis. This combined layer formed a coating material that could be useful for improvement of the selectivity of the solutes in an electrical field. We reasoned that the interaction of the solutes and the modified capillary wall occurred mainly via ionic interactions with the charged moieties of CNTs. The single-walled CNT modified capillaries were very stable and could be used for over 200 repeated analyses without compromising its analytical performance.

Nanoscale surface characterization of biphasic calcium phosphate, with comparisons to calcium hydroxyapatite and ß-tricalcium phosphate bioceramics.

OBJECTIVES: It is our aim to understand the mechanisms that make calcium phosphates, such as bioactive calcium hydroxyapatite (HA), and biphasic calcium (BCP) and ß-tricalcium (ß-TCP) phosphates, desirable for a variety of biological applications, such as the filling of bone defects. METHODS: Here, we have characterized these materials by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR), time-of-flight secondary ion mass spectroscopy (TOF-SIMS) and laser granulometry. RESULTS: SEM shows clearly that BCP is a matrix made of macro-organized microstructure, giving insight to the specially chosen composition of the BCP that offers both an adequate scaffold and good porosity for further bone growth. As revealed by laser granulometry, the particles exhibit a homogeneous size distribution, centered at a value somewhat larger than the expected 500 µm. XPS has revealed the presence of adventitious carbon at all sample surfaces, and has shown that Ca/P and O/Ca ratios in the outer layers of all the samples differ significantly from those expected. A peak-by-peak XPS comparison for all samples has revealed that TCP and BCP are distinct from one another in the relative intensities of their oxygen peaks. The PO3(-)/PO2(-) and CaOH+/Ca+ TOF-SIMS intensity ratios were used to distinguish among the samples, and to demonstrate that the OH- fragment, present in all the samples, is not formed during fragmentation but exists at the sample surface, probably as a contaminant. CONCLUSIONS: This study provides substantial insight into the nanoscale surface properties of BCP, HA and ß-TCP. Further research is required to help identify the effect of surfaces of these bioceramics with proteins and several biological fluids. CLINICAL RELEVANCE: The biological performance of implanted synthetic graft bone biomaterials is strongly influenced by their nanosurface characteristics, the structures and properties of the outer layer of the biomaterial.

The differential detection of methicillin-resistant, methicillin-susceptible and borderline oxacillin-resistant Staphylococcus aureus by surface plasmon resonance.

Two hundred fifty Staphylococcus aureus clinical isolates were studied to determine their susceptibilities to ß-lactam antibiotics. Among these isolates, 16 were methicillin-sensitive S. aureus (MSSA), 207 were methicillin-resistant S. aureus (MRSA) and 27 were borderline oxacillin-resistant S. aureus (BORSA). Currently, the reported mechanism of methicillin resistance in S. aureus is the production of a distinctive penicillin binding protein 2a (PBP2a), which exhibits low affinity toward ß-lactams. A surface plasmon resonance biosensor was evaluated for its ability to identify MRSA and to distinguish these strains from MSSA and BORSA, by specifically detecting PBP2a. We found that the system permits label-free, real-time, specific detection of pathogens for concentrations as low as 10 colony forming units/milliliter (CFU/ml), in less than 20 min. This system promises to become a diagnostic tool for bacteria that cause major public concern in clinical settings.

The effect of ethylene oxide sterilization on the surface chemistry and in vitro cytotoxicity of several kinds of chitosan.

The surfaces of three chitosan samples, differing only in their degrees of deacetylation and of carboxyethyl chitosan were chemically characterized by X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectroscopy, X-ray diffraction, and Fourier transform infrared, both before and after sterilization with ethylene oxide. Unexpected elemental ratios suggest that surface chemical modification occurred during the processing of the original chitin, with further surface modification on subsequent sterilization, despite previous reports to the contrary. Cell viability was evaluated by direct contact methyl thiazole tetrazolium and lactate dehydrogenase assays between the chitosan particles and A549 human epithelial cells, which demonstrated that the modifications incurred on sterilization are reflected in biocompatibility changes. All the samples were found to be biocompatible and nontoxic before sterilization and remained so subsequently.

The effect of ethylene oxide sterilization on the surface chemistry and in vitro cytotoxicity of several kinds of chitosan.

The surfaces of three chitosan samples, differing only in their degrees of deacetylation and of carboxyethyl chitosan were chemically characterized by X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectroscopy, X-ray diffraction, and Fourier transform infrared, both before and after sterilization with ethylene oxide. Unexpected elemental ratios suggest that surface chemical modification occurred during the processing of the original chitin, with further surface modification on subsequent sterilization, despite previous reports to the contrary. Cell viability was evaluated by direct contact methyl thiazole tetrazolium and lactate dehydrogenase assays between the chitosan particles and A549 human epithelial cells, which demonstrated that the modifications incurred on sterilization are reflected in biocompatibility changes. All the samples were found to be biocompatible and nontoxic before sterilization and remained so subsequently. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2013.